The conventional wireless communication system includes a mobile station (MS) and a base station (BS) providing a service in a specific region (i.e., a cell). Quality of a signal transmitted through a wireless channel between the MS and the BS may be affected by changes in a wireless environment. In particular, due to various factors in a surrounding environment, such as scatters, movement of the MS, or the like, the wireless channel changes over time. In addition, there is a restriction in terms of distance since reception power is rapidly decreased in proportion to a distance between wireless communication entities. Therefore, in general, the MS can communicate with the BS when the MS is located within the coverage of the BS. As such, a maximum transfer rate, a throughput of an intra-cell user, and a throughput of an entire cell are decreased between the BS and the MS due to several factors such as scatters, a movement speed of the MS, a distance between transmission and reception, or the like. For example, when the MS is located in a cell boundary or when an obstacle such as a building exists between the MS and the BS, communication quality between the MS and the BS may not be satisfactory.
As an effort to overcome the aforementioned problem, the wireless communication system may employ a relay station (RS). The RS is a device for relaying a signal between the MS and the BS. The RS employs several techniques to compensate for deterioration of signals transmitted between the BS and the MS, and thus the wireless communication system is expected to obtain throughput improvement, coverage expansion, or the like.
When the wireless communication system employs the RS, there is a problem in a method of transmitting a scheduling request between the RS and the BS. In particular, the problem arises when a hybrid automatic repeat request (HARQ) is applied between the RS and the BS. The HARQ is a scheme in which channel coding of a physical layer is combined with the conventional ARQ scheme to improve transmission efficiency in data processing. When using the HARQ, a data transmission error is handled in the physical layer. Therefore, error correction can be achieved faster than the case of using the ARQ performed in a higher layer.
The HARQ can be classified into a synchronous HARQ and an asynchronous HARQ. The synchronous HARQ is a scheme in which data is retransmitted at a time known to both the BS and the MS. The synchronous HARQ can reduce signaling required for transmission of data such as an HARQ process number. The asynchronous HARQ is a scheme in which a resource is allocated at any time for retransmission. The asynchronous HARQ requires exchange of resource allocation information needed for transmission of a scheduling request signal and data. 3rd generation partnership project long term evolution (3GPP LTE) uses the synchronous HARQ in uplink transmission and uses the asynchronous HARQ in downlink transmission.
In the wireless communication system employing the RS, a radio resource used between the BS and the RS is limited and opportunity of using the radio resource is variable. This is because the radio resource is allocated even to a link between the RS and an MS connected to the RS. This is also because signal transmission and reception cannot be simultaneously performed in the link between the BS and the RS and the link between the RS and the MS connected to the RS.
It is problematic when the synchronous HARQ applied to the link between the BS and the MS is directly applied to the link between the BS and the RS. In addition, it is ineffective to directly apply the conventional asynchronous HARQ in which the scheduling request and the resource allocation information are repetitively exchanged.